What do these codes mean?

complete guess, but i don't think your reader is adequate

 

Brake Booster/Actuator Code 1253 is the major concern. Its a really big safety issue you should have checked out at a dealer. Here's the rundown:

I may be a bearer of bad news in that 1253 sounds like the dreaded brake booster and actuator problem. Hopefully I am wrong.

Prius is 99% brake by wire except for a total failure of those two parts. The booster creates hydraulic pressure with an electric (buzzing) pump and stores it in a hydraulic accumulator. The brake actuator is a combination master cylinder, brake ecu, traction control and abs module. The brake ecu is on the network and helps to determine if hydraulic braking is needed or if regeneration of electrical power is sufficient to slow the vehicle. It is also controlling traction control and abs. So a common problem is the booster starts to fail causing it to run for longer and longer times creating the pump buzzing sound. It is located near the actuator on the drivers side engine firewall conveniently tucked under the windshield wiper assembly. On mine the booster would run every 15 seconds or so to maintain brake hydraulic pressure. It will also run when you first open the driver's door after it has been sitting for a few hours. It will be louder as you are still outside of the car and can hear it more directly. The booster has a sealed nitrogen chamber separated from the brake fluid by a flexible metal diaphragm, something like a water well pressure tank. The metal diaphragm starts leaking and nitrogen gets into the brake actuator (master cylinder/ecu/abs) and causes it to fail as well. The booster is running a lot but you just don't hear it at speed because of other noises.

Now the bad part. Sometimes they won't throw a code or even cause the ABS/Traction Control lights (especially after a code reset) because it takes about five minutes of continuous running to trip a specific code. Sometimes a complete Techstream algorithm brake flush (to get into all the actuator passages) will make the problem go away for a day or so.

Now for the sad part. Dealers and Prius mechanics know this is a chronic problem especially in high mileage cars. They have replaced hundreds of these per mechanic. Toyota has a free replacement program for most Gen 3 Prius systems EXCEPT for the Prius v. At first they would replace only the booster but soon found they usually needed to replace the actuator as well. The job takes many hours because of access. For Prius v owners, its used or new repairs at our expense. It has a book price of around $4k at most dealers, I was quoted $2250 at my dealer. They are a hard pair of parts to get to especially on a v. I had an independent Prius mechanic change mine with used for $1200 and he warranted it for a year. Works good now.

Yes there is a failsafe mode should the accumulator or actuator fail 100%. A pair of normally closed solenoids in the actuator fail closed and your brake petal gets real hard to push as you are now operating the brakes directly with no power brakes.

From Toyota with the brake actuator/ecu shown on top:

 

The description above is more-or-less ok except for a very common terminology confusion: the booster pump is not the booster.

In the description above, you need to read booster pump everywhere booster is written.

The booster is part of the master cylinder and, as such, it is part of the other (actuator) assembly. In fact that actuator assembly is often called the "brake booster assembly" in Toyota documents and parts lists. That's also the name used in T-CP-D0H-A510-D, where the same illustration above can be found, but without the name of the upper part erased:



If you look at it schematically, the booster pump assembly is just the two components drawn in the top right corner here ("accumulator" and "pump motor"). The booster is a small chamber at the rear of the master cylinder where the pressurized fluid boosts your pedal effort by pushing on the piston in the same direction you are.



Yes, the nomenclature is confusing, but that just makes it more important for us to be careful not to make it worse.

One also has to be very careful when shopping for these items, especially aftermarket, because sellers mix up the names all the time too.

But anyway...

We've gotten very far ahead of this car's story.

The C1253 code is specifically a code to check out the relays that supply the electric power to the pump. Also, there are about nine different subcodes that a proper reader can retrieve that will give more detail about what exactly was detected. It can still turn out that either the pump/accumulator, or the booster/actuator, or even both, need replacement, but it can also still turn out to be something much simpler.

Further diagnosis is called for, before assuming the worst.

A little more about the failure modes covered in the past recalls and service campaigns...

The above post describes an issue where the metal bellows in the accumulator can leak nitrogen gas into the hydraulic system. That has happened, and it specifically happened in a certain run of accumulators where the metal bellows ended up slightly undersize, so it banged around in the canister while driving, picking up stress cracks. Those accumulators were replaced in a recall. (Sometimes you see what look like the old ones, up for resale on ebay.)

There has also (for liftback anyway, I guess not the v) been a warranty extension for a small internal hydraulic leak in the actuator assembly. There are a lot of little valves in there, and if something doesn't seal fully, brake fluid can constantly slowly leak past it. It doesn't escape the system and make puddles under the car, it just flows back into the reservoir. That kind of issue can also cause the pump to have to run often to maintain accumulator pressure, but it should not be confused with the gas-leaking-from-bellows issue.

And again, this car still just needs somebody to find out what the actual issue is; it might not be either of those.

 

Actually the two separate parts do have "booster" in their names depending on where you read it in Toyota materials. On gen2 Prii it was one assembly. And yes the v has a different actuator/master cylinder than the same years hatchback. It could be a relay but 1253 usually means the booster/accumulator and the actuator/master cylinder/brake ecu. Either way I would suggest he take it to a dealer. Thumbnails below are the parts used in my Prius v. One is in progress while they were being replaced while the other two are the online parts from a Toyota dealer.

 

That's absolutely true, as clearly seen in the discussion and the illustrations above. There is a booster, and there is a booster pump. They are not the same thing.

Gen 2 was the oddball generation: it had a booster pump but no booster. Gen 2 was more brake-by-wire than any of the generations before or since. Instead of using the pressurized fluid in a boost chamber of the master cylinder to assist you, it just measured your effort and computed what fluid pressure to send straight to the brakes.

Because it was that much more dependent on the computer doing its part, Gen 2 also had a big capacitor box in back to supply electric power to the brake system if other electrical power failed.

It was the only generation to have that. Outside of Gen 2, even if electric power fails, you still have hydraulic brakes and even, enough for 20 or 30 strokes, boosted hydraulic brakes, using up the pressurized fluid in the accumulator. You don't get to the really-hard-pedal non-boosted brakes until stuff has all failed and you have used up your 20 or 30 strokes.

 

Please recommend repair in Houston area or advice. This may be goodbye to the Prius | PriusChat

Probably better to post the above in this thread. Commenting on the new thread:

How many miles on it. What's it's general condition?